A sensitive
sandwich electrochemiluminescence immunosensor was
established by employing graphene oxide-PEI-carbon quantum dots (CQDs)-Au
nanohybrid as probe to measure carbohydrate antigen 15-3 (CA15-3),
a breast cancer biomarker. In this work, nanocomposites of Ag nanoparticles
and polydopamine (AgNPs-PDA) were synthesized by redox reaction between
dopamine and Ag+. The nanocomposite with high surface area
can provide an efficient substrate for immobilizing initial antibody
(Ab1). Carbon quantum dots (CQDs) are fixed on polyethylenimine-functionalized
graphene oxide (PEI-GO) by amide bonds. Au nanoparticles are modified
on CQDs-decorated PEI-GO substrates. The secondary antibody (Ab2)
was immobilized by AuNPs/CQDs-PEI-GO composite. CQDs can be assembled
onto the surface of an electrode by incorporation of CA15-3 with Ab1
and Ab2. Under the synergistic action of AgNPs, polydopamine, AuNPs,
and PEI-GO, the ECL signal of CQDs is greatly amplified as an excellent
conductive material to facilitate electron transfer rate and further
increase electrochemical detection capability. Under optimal conditions,
the fabricated immunosensor showed a linear concentration range from
0.005 to 500 U mL–1, with a detection limit of 0.0017
U mL–1 (signal-to-noise ratio of 3) for CA15-3.
The designed ECL immunosensor displayed receivable accuracy, excellent
stability, and high specificity. The results of the detection of human
serum samples are satisfactory, revealing that the method offers a
potential application for the clinical diagnosis of tumor markers.
A hydrothermal strategy for preparing boron and nitrogen codoped carbon quantum dots was studied using the precursors of p-amino salicylic acid, boric acid and ethylene glycol dimethacrylate. The boron and nitrogen codoped carbon quantum dots have high fluorescence intensity, good monodispersity, high stability, superior water solubility, and a fluorescence quantum yield of 19.6%. Their average size is 5 nm. Their maximum excitation and emission wavelengths are 380 and 520 nm, respectively. Permanganate (MnO 4 − ) quenched boron and nitrogen codoped carbon quantum dots fluorescence through inner filter effect and static quenching effects. The linear relation between quenching efficiency and MnO 4 − concentration ranged from 0.05 to 60 μmol/L with a detection limit of 13 nmol/L. In the presence of captopril, MnO 4 − was reduced to Mn 2+ and the fluorescence of boron and nitrogen codoped carbon quantum dots was recovered. The linear range between recovery and captopril concentration was from 0.1 to 60 μmol/L. The limit of detection was 0.03 μmol/L. The developed method can be employed as a sensitive fluorescence sensing platform for MnO 4 − . It has been successfully used for captopril detection in mouse plasma.
S,N-Codoped carbon quantum dots (SNCQDs) with a quantum yield (QY) of 23% have been synthesized using lotus root as a carbon source and glutathione (GSH) as a nitrogen and sulfur source. The obtained SNCQDs exhibited many excellent features such as a simple preparation process, high fluorescence QY, satisfactory photostability, superior water solubility, and biocompatibility. The SNCQDs combined with Cu 2+ were used as a novel off− on nanoprobe for 6-thioguanine (TG). Initial fluorescence is significantly quenched in this sensing system via electron transfer from SNCQDs to Cu 2+ . Fluorescence is recovered after adding TG owing to Cu 2+ −TG complex formation between Cu 2+ and TG. A novel off−on fluorescent nanoprobe was presented for highly sensitive determination of TG. Under optimal conditions, the nanoprobe exhibited a wide linearity range of 0.005−80 μmol/L for TG and a detection limit of 1.6 nmol/L. The designed off−on nanoprobe was successfully utilized for detecting TG in plasma and urine of a leukemia patient and imaging of TG in living T24 cells.
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